1. Field of the Invention
This invention relates to a secretory protein, kappa-casein (.kappa.-casein), which inhibits the attachment of human rotavirus (HRV) to mammalian cells.
2. Description of the Prior Art
Rotaviruses are the most important viral agents causing gastroenteritis in children living in both developing and developed countries (Yolken et al, "Human Milk Mucin Inhibits Rotavirus Replication and Prevents Experimental Gastroenteritis", Journal of Clinical Investigation 90, 1984-1991, 1992). Rotaviruses also cause diarrhea in nursing homes and day care centers, among travelers, in adults who have contact with children, and in immunocompromised patients.
Breast feeding provides some protection against enteric infections by pathogens when breast-fed infants are compared with bottle-fed babies. Studies of children living in developing and developed countries have shown that breast-fed infants have fewer episodes of gastroenteritis than bottle-fed infants. Breast feeding can also lessen the severity of diarrhea and vomiting associated with enteric diseases. However, breast-feeding does not provide total protection against infection and rotavirus infection has been observed in breast-fed infants.
No single factor has been found to be entirely responsible for the protective effect of breast feeding. It is believed that antibodies play a role, however, the level of anti-rotavirus antibody in human milk does not correlate with the degree of protection afforded by the milk. This suggests that non-immunoglobulin factors contribute to the protective effect of breast milk, and investigations have been undertaken to identify these factors.
Yolken et al. report a nonimmunoglobulin natural substance, milk mucin, that inhibits the replication of rotavirus. Mucin is a sialic acid-containing glycoprotein. In this report, Yolken et al. demonstrate that mucin and mucinous components found in human milk show anti-rotaviral activity. Using purified milk mucin components in a solid-phase binding assay, Yolken et al. first showed mucin binding to African Green Monkey Kidney (MA-104) cells infected with human and simian strains of rotavirus. Using tissue culture techniques they next showed that a fraction of human milk, subsequently identified as human milk mucin complex, inhibited rotavirus replication. This was further demonstrated by showing that this fraction bound specifically to cells infected with rotavirus. When the active fraction was desialylated by chemical hydrolysis, there was a substantial decrease in binding to the rotavirus infected cells. This indicates that in the antiviral system reported here sialic acid is necessary for anti-rotaviral activity. Yolken et al. did not find evidence of rotavirus inhibitory activity in the lipid fractions of milk.
Yolken et al. also demonstrated the efficacy of mucin-containing milk components in preventing experimental rotavirus gastroenteritis in suckling mice.
WO 94/09651 (Newburg et al.,"Anti-Diarrheic Product and Method of Treating Rotavirus-Associated Infection") discloses a product containing an anti-diahrreal agent, such as the milk mucin complex and its components, which can bind rotavirus, and a method of inhibiting rotavirus infection in mammalian cells by exposing them to these agents.
U.S. Pat. No. 5,147,853 (Dosako et al., "Infection Protectant") discloses a method for preventing adhesion of E. coli to human epithelial cells by treating them with .kappa.-casein, a sialic acid-conjugated protein derived from cow's milk.
The prevalence of rotavirus infection in the groups at risk, especially infants and children, and the seriousness of its effects attests to the need for an effective treatment. It is of particular importance to develop methods for prevention and treatment of rotavirus infection that have no adverse side effects.